Diffractometer and method for diffraction analysis

ABSTRACT

Diffractometer and method for diffraction analysis making use of two Euler cradles, a primary and a secondary Euler cradle. The primary Euler cradle supports a source of a radiation beam, having a collimation axis, and a radiation beam detector, having a reception axis, said collimation and reception axis, conveying in a centre of the diffractometer which is fixed with respect to the primary Euler cradle. The source and detector are adapted to move along the primary Euler cradle. The secondary Euler cradle supports the primary Euler cradle and is arranged to rotate the latter.

FIELD OF THE INVENTION

The present invention concerns a diffractometer, in particular a x-raydiffractometer. In more detail, it concerns a diffractometer performingnon destructive tests on elementary components, which are not suited (orallowed) for being analysed by traditional diffractometers or even oncomponents that cannot be displaced from their original location.

PRIOR ART

Diffraction techniques are widely used in the field of analysis ofmaterial structure. The obtainable information by this technique areimportant in several field as chemistry, metallurgy and metallography,extractive industry, transportation, environment, aeronautics,aerospace, buildings and even conservation of cultural heritage.

Several types of radiation are used for diffractometric analysis. Verycommon are the diffraction techniques by x-ray, electrons and neutrons.Particularly important are the techniques of x-ray diffraction.

Generally this kind of equipment are used to detect diffraction frompowders or polycrystalline solids. Analysis on polycrystalline solidsare especially interesting when investigation is required for componentsof industrial implants and/or implant in exercise.

These equipment require a x-ray source, a specimen stage and a x-raydetector. The specimen is requested to rotate, so that its surface isilluminated by the x-ray beam, coming from the source under differentangles. Specimen and detector are requested to rotate simultaneously(optionally) at distinct rate so that their relative position allow thedetector for receiving the diffraction beam form the crystallographicplanes which are in the right position for reflection.

The x-ray diffractometry is useful to obtain information in field ofchemical composition, physical and mechanical characteristics ofspecimens (presence of residual stress or compression) of metalmanufactured or other material. It is useful even for precociousdetection of defects or damages of crystalline structure, for example,in welded components or under load or fatigue. Generally, this stresscauses preferred orientation of crystalline lattice that can be detectedby x-ray diffraction when particular procedures are adopted. Thistechnique is useful even to analyse fibrous structures and glasses todetermine the state of conservation and the chemical and physicalcharacteristics.

It is sometimes useful to investigate by non destructive testing thelattice structure of components in implants on exercise. In this case,it is often difficult or impossible to obtain specimens for intraditional analysis and laboratory tests. Often, it happens that thecomponent or the implant under analysis can not be moved. For thisreason, there is the necessity of a diffractometer, and in particular, ax-ray diffractometer that can be easily used without moving anystructure or component of the implant. It's important that thisdiffractometer permits to obtain a considerable range of information(i.e. equivalent to the laboratory diffractometers to analyse powdersand polycrystalline materials). In particular, it is useful to recognisethe presence of stress, preferential orientations, structural defects ofthe material that constitute the component analysed, avoiding that theparticular working condition of the diffractometer will constitute alimit for the attainable information. It means that it is necessary todevelop a diffractometer that is useful for being used in place andimprove the performance of the traditional laboratory diffractometers.

SUMMARY OF THE INVENTION

The above mentioned problems are overcome by a diffractometercomprising:

-   -   an analytical unit supporting a radiation source having a        collimation axis; and a radiation detector having a reception        axis, said collimation and reception axis converging in a        centre, named centre of the diffractometer, which is fixed with        respect to the analytical unit;    -   means for moving said analytical unit;    -   means for rotating said source and detector around said centre        of the diffractometer

Preferably, said means for moving said analytical unit permit to changethe position in space of the centre of diffractometer.

According to a favourite embodiment of the invention, the diffractometeris a x-ray diffractometer.

Preferably, said means for rotating said source and detector aresuitable to rotate source and detector, so that the axis of collimationand reception are contained in a equatorial plane. This plane is fixedwith respect to the analytical unit.

According to a favourite embodiment of the invention, said analyticalunit is supported by a supporting and movement structure and means areprovided for moving said analytical unit with respect to the structureof support and movement, so that the analytical unit can rotate aroundan axis, called equatorial axis, contained in the equatorial plane andpassing through the centre of the diffractometer. This fact correspondsto a rotation of the equatorial plane around the equatorial axis. Thistype of rotation is advantageously possible for an arc of at least 10°,preferably of at least 20° or even far higher values, for particularanalytical necessity.

According to a preferred embodiment of the invention, the movement ofthis analytical unit with respect to the support and movement structure,permits the rotation of the equatorial plane with respect to theequatorial axis, without changing the axis position in the space.

The plane perpendicular to said equatorial axis and containing thecentre of the diffractometer, is fixed with respect to the analyticalunit, and it's called axial plane. This plane can constitute a symmetryplane for said analytical unit.

As “source collimation axis” is commonly defined the axis of theradiation beam that the source can emit and as “reception axis”, theaxis of the radiation beam that can be detected by the detector.

The invention also concerns a method of diffractometry, preferably ofx-ray diffractometry comprising positioning a diffractometer aspreviously described with the centre of the diffractometer at a point ofthe surface of an element to be analysed.

According to a possible embodiment of the invention, the axial plane canbe advantageously placed perpendicularly with respect to the surface ofthe analysed element at the point coincident with the centre ofdiffractometer.

According to an embodiment of the invention said analysed element is notmechanically connected to the diffractometer, with which, morepreferably, is not even in contact.

LIST OF THE FIGURES

FIG. 1 represents schematically the lateral view of a x-raydiffractometer, according to the present invention.

FIG. 2 represents schematically the frontal view of the diffractometerof FIG. 1.

FIG. 3 represents schematically a detail of the diffractometer of FIG.1, more specifically, the extremity of the diffractometer that includesthe first analytical unit supporting the source and the x-ray detector.

FIG. 4 represents schematically the lateral view of the detail of thediffractometer of FIG. 1 comprising the first analytical unit supportingthe source and the x-ray detector and the structure for supporting andmoving the analytical unit.

FIG. 5 represents schematically an articulation able for moving saidanalytical unit in the space, according to a particular embodiment ofthe invention.

DETAILED DESCRIPTION OF A POSSIBLE FORM OF IMPLEMENTATION

As an example a x-ray diffractometer according to the present inventionis described.

The FIG. 1 shows a lateral view of a x-ray diffractometer, according tothe present invention. The equipment includes a base (1), that can beequipped with two wheels or other means for transportation andpositioning and can also contain an electric generator capable ofgenerating the energy required for the use,) a tank of cooling liquidfor the x-ray source and the electric components for positioning themovable parts and collecting data from the measurement equipment andalso to process these data.

The equipment includes a support (3), an arm (4) supported by saidsupport (3) and rotatable with respect to the arm, to permit a verticalpositioning of the extremity (6) that includes the analytical unit,supported by the arm (4). Locking devices (5) permit to fix the arm (4)positioned with respect to the support (3). The extremity (6), alsovisible in the FIG. 2 and FIG. 3, includes a x-ray souse (7), a x-raydetector (8) and other positioning devices. These devices include theelement (9), called primary Euler cradle, which may advantageously be inthe form of a circular arch, devoted to support the x-ray source (7) andthe detector (8). In the described case, the primary Euler cradle is theanalytical unit. Source (7) and detector (8) can be conveniently movedalong the primary Euler cradle (9). For each position reached on theprimary Euler cradle by source and detector, the source collimation axis(11) and the reception axis (10) are always directed towards a point(12), which is the centre of the diffractometer (12) and canadvantageously coincide with the centre curvature of the primary Eulercradle (9).

The axes (10) and (11), can thus rotate the centre (12) in a plane, theequatorial plane, that is substantially parallel to the primary Eulercradle (9). In the FIG. 3 the equatorial plane coincides with the planeof the drawing, the axial plane is perpendicular to it, theirintersection is the axis (13), called exploration axis.

According to a preferred embodiment of the invention, said primary Eulercradle (9) is conveniently supported by a structure supporting andmovement (14), called secondary Euler cradle. A special system permitsto the primary Euler cradle (9) to be moved with respect to thesecondary Euler cradle (14) to execute a rotation around the equatorialaxis (15). This equatorial axis (15) is contained in the equatorialplane and is perpendicular to the exploration axis (13). In this way,the whole equatorial plane can rotate of a certain angle with respect tothe equatorial axis (15), and thus the collimation axis (11) and thereception axis (10) can rotate because the source (7) and the detector(8) are supported by the primary the Euler cradle (9).

FIG. 4 shows a lateral view of the extremity (6) that includes the twoEuler cradles, and shows a possible implementation of the articulationmechanism of the primary Euler cradle (9) with respect to the secondaryEuler cradle (14). The primary Euler cradle (9) includes two cog arcs(21) and (21′), suitably joined. The source (7) and the detector (8)move along these arcs through a gear moved by electrical motors 20 and20′, which are part of source and detector. a support (22), jointed tothe primary Euler cradle (9), supports it to the secondary Euler cradle(14). The support (22) has a portion (23) having a dovetail shapedstructure (24), said structure running in a correspondent cavity (25)(dashed in FIG. 4) of the secondary Euler cradle (14), thus permittingthe movement of rotation of the equatorial plane, as above discussed. Anendless screw (not shown) is set parallel to the axis (26) and moved bya motor (27) and mates with a correspondent thread obtained on the uppersurface (28) of the dovetail structure (24). This endless screw promotesthe rotation of the primary Euler cradle (9). This, like other types ofmechanism can be easily implemented by a technician of the field.

A series of movement devices for positioning in the space the extremity(6) that include the two Euler cradle is also foreseen.

With reference to FIG. 2, the system (16) equipped with a motor 30,permits the complete rotation, around the arm axis (4) of this extremity(6). This permits a very advantageous instrument positioning, and alsoprovides the possibility of exploring the material to be analysed alongdifferent directions.

With reference marks (31) and (32), two slides are identified; theypermit mutually perpendicular translation movements; this movement isalso perpendicular to the arm axis (4); these slides are also moved byspecial motors.

The motor (33), trough a screw mechanism, permits the translation of thearm 4 long its axis.

Other moving devices could be provided to facilitate the positioning ofthe extremity (6). For example an articulation can be provided,preferably between the device (16) and the system of slides (31) and(32), permitting a rotation around an axis perpendicular to the arm axis(4). In FIG. 5, this articulation is schematically represented by mark(35) and is set above the pivot (16) (schematically indicated). Thisarticulation permits a rotation of 180° and can be conveniently moved bya special motor.

Instead of the support (3) a vertical support can be provided, alongwhich arm (4) may translate vertically thanks to a special device. Thisvertical support could rotate around its axis, thus giving a furtherfreedom degree to the structure positioning. It's apparent thatequipment can be implemented with different kinds of moving devices,according to the investigation requirements.

On the primary Euler cradle (9) pointing devices can be provided forpositioning the instrument correctly with respect to the element underinvestigation. As described above, this element under analysis may be acomponent of an operating structure, for example part of an industrialplant, or also an element too big dimensions to be moved, and thatrequires a not destructive structural control. The pointing device caninclude two lasers fixed on the primary Euler cradle and pointed towardsthe centre of the diffractometer (12), and a telecamera, also fixed onthe primary Euler cradle and pointed along the axis of exploration (13).The overlap of the two spots projected by the laser on the surface ofthe element analysed, and their shape will is indicate the correctpositioning of the equipment with respect to the element analysed.Advantageously, the moving part may be moved by special motors,controlled by electronic systems. These systems can collect data fromthe pointing device and manage completely the positioning of theequipment.

Also the movement of the source and of the x-ray detector may be managedby an electronic system, as well as the movement of the primary Eulercradle can be electronically controlled respect to the secondary.

Source and detector can be of different types, chosen among thosecommonly used in the diffraction field. These types include all thesuitable collimation system (slits, beams conditioning, and alsomonochromators if necessary). In particular, the detector can include aslide system that permits the movement of the collimation system (i.e.“capillary optic”, “poly-capillary”, etc.) along the reception axis ofthe beam, from and towards the centre of the diffractometer.

The choice depends on the type of radiation used and on thecharacteristic of the element analysed, as well as constructive problemsof the equipment. In particular, in the case of x-ray diffraction, thedetector can be either a scintillation detector, a solid state or anyother known device. According to a possible embodiment, a ionisationdetector of gas, such as a Geiger counter, can be used because of theirreduced dimensions. According to a preferred embodiment of the inventionit's possible to use a Geiger counter in its field of proportionality,also called proportional counter. Furthermore, source and detector canbe equipped with devices that permit their shifting the collimation andreception axes respectively, to regulate, outside said source anddetector, the optic path of the beam incident on the material to beanalysed and diffracted beam, according to operating requirements.

The dimension of the equipment can be chosen in relation to theapplication the instrument is built for and be such that all the devicesare suitably supported. In particular, as far as the primary Eulercradle is concerned, they must be sufficient to adequately supportsource and detector in relation to their dimensions and to permit asufficient excursion along the primary Euler cradle itself. It's alsoimportant to keep in mind that, by increasing the size, the requiredpower of the motors increases, to move the structures without the riskof vibration.

For example, it has been possible to implement an equipment as describedwith an external radius of the primary Euler cradle of about 22 cm, anexcursion of source and detector, of the proportional ionisation kind,of about 135°, with a distance of about 11 cm between the centre of thediffractometer and the source and between the centre of thediffractometer and detector. Trough analysis of reference specimen,results were obtained in armony with those of traditionaldiffractometers. The structure can also include electric connection andconnections for transmitting data between the electronic control systemsand the various devices of movement or detection above described, andalso pipes for the cooling liquid for the source of x-ray.

According to a possible method of using the diffractometer, the latteris placed so that a point of the surface of the element to be analysedis at the centre of the diffractometer (12). When starting, that surfaceshall be perpendicular to the exploration axis (13); when the surface isnot flat, the plane tangent to the surface, called specimen plane, shallbe perpendicular to the exploration axis. Thus the collimation axis (11)forms an angle θ with the specimen plane. The reception axis (10) willform an angle θ with the specimen plane and 2θ with respect to thecollimation axis. The system is thus able to detect the rays reflectedby families of crystallografic planes, that have a interplanar distanced that, for an angle θ correspondent to the relative position of thesource and detector, satisfies the Bragg's law nλ=2d*sin θ, where n is awhole number and λ the wavelength of the x-ray beam emitted from thesource.

According to a possible operating method, the collimation axis (11) andthe reception axis (10), perform the above mentioned rotation by keepingthemselves symmetric with respect to the exploration axis (13); thus, itis possible to detect the diffraction beam from various families oflattice planes satisfying the Bragg law at different angles θ.

When the specimen is a polycrystalline solid with enough small crystals,as it is common, the various families of planes may be randomly orientedin all the directions. So by scanning various angles θ, the variousfamilies of planes that satisfy Bragg law can be detected. By a rotationof the equatorial plane, around the equatorial axis (15), as abovementioned, and by keeping unvaried the position of the source anddetector with respect the axis of exploration (13) (that will be rotatedof ω together with the equatorial plane), The equatorial plane will beno longer perpendicular to the specimen plane. It is thus possible toscan again the different angles θ, and detect signals from the planesinclined of an angle ω with respect to the specimen plane. Thecomparison at different θ angles of diffraction intensities at the sameθ angle (corresponding to plane families with the same interplanardistance), give an information on the possible preferred orientations inthe crystalline structure. This is equivalent to explore for a certainarc the Debye circle.

Alternatively, the collimation and reception axes can be keptsymmetrical with respect to an axis laying on the equatorial plane anddifferent from the exploration axis to analyse families of planes withdifferent inclinations with respect to the exploration axis. This isimportant when monocrystalline materials have to be analysed, or if it'simpossible to position the exploration axis perpendicular to thespecimen plane, or when special directions in the materials have to beanalysed.

The number of different possible positioning of the equipment confers agreat versatility to the use of the diffractometer.

When the specimen can be at least partly moved or orientable in thespace the analysis opportunities are extended, so that a range ofinformation that are comparable to those obtained from traditionallaboratory instruments may be obtained, such as single crystalinstruments which have the highest number of freedom degrees fororienting the specimen in the space.

It has been described in particular a diffractometer, and a method forits use, in which the radiation used are x-ray. This constitutes apreferred embodiment of the invention. Anyway, with equipment built withspecial dimension and features, it's possible to use different kinds ofsources and detectors of other kinds of radiation, such aselectromagnetic, acoustics or consisting of particle beams.

1. A diffractometer comprising: an analytical unit supporting a sourceof a radiation beam having a collimation axis and a radiation beamdetector having a reception axis; said collimation and reception axesconverging at a centre of the diffractometer; said centre of thediffractometer being fixed with respect to said analytical unit; meansfor moving said analytical unit; means for rotating said source and saidradiation beam detector around said centre of the diffractometer so thatsaid collimation axis and said reception axis are kept in an equatorialplane, fixed with respect to said analytical unit; a support andmovement structure supporting said analytical unit; means for movingsaid analytical unit with respect to said support and movement structureso that said analytical unit can rotate around an equatorial axiscontained in said equatorial plane and passing through said centre ofthe diffractometer; said means for moving said analytical unit withrespect to said support and movement structure permitting the rotationof the equatorial plane around said equatorial axis, without saidsupport and movement structure changing its position.
 2. Thediffractometer according to claim 1, wherein said means for moving saidanalytical unit enables rotation of said analytical unit around an axisperpendicular to said equatorial axis.
 3. The diffractometer accordingto claim 1, wherein said source is a source of electromagneticradiation, acoustic radiation, or radiation consisting of particle beamsand said detector is a detector of electromagnetic radiation, acousticradiation, or radiation consisting of particle beams.
 4. Thediffractometer according to claim 1, wherein said source is a x-raysource and said detector is a x-ray detector.
 5. The diffractometeraccording to claim 1, wherein said means for moving said analytical unitpermit to change a position of said centre of the diffractometer byrotation or translation of said analytical unit.
 6. The diffractometeraccording to claim 1, wherein said equatorial axis is perpendicular to asymmetry plane of said analytical unit.
 7. The diffractometer accordingto claim 1, wherein the rotation around said equatorial axis is long anarc of at least 10°.
 8. The diffractometer according to claim 3, whereinsaid detector is a proportional ionization counter.
 9. Thediffractometer according to claim 1, comprising a pointing device placedon said analytical unit for positioning said analytical unit withrespect to an element to be analysed.
 10. The diffractometer accordingto claim 9, wherein said pointing device comprises two lasers and atelecamera.
 11. The diffractometer according to claim 1, wherein saidanalytical unit is formed as a circular arc.
 12. A diffractometry methodcomprising: positioning a diffractometer including an analytical unitsupporting a source of a radiation beam having a collimation axis and aradiation beam detector having a reception axis, the collimation andreception axes converging at a centre of the diffractometer, the centreof the diffractometer being fixed with respect to the analytical unit,means for moving the analytical unit, means for rotating the source andthe radiation beam detector around the centre of the diffractometer sothat the collimation axis and the reception axis are kept in anequatorial plane, fixed with respect to the analytical unit, a supportand movement structure supporting the analytical unit, means for movingthe analytical unit with respect to the support and movement structureso that the analytical unit can rotate around an equatorial axiscontained in the equatorial plane and passing through the centre of thediffractometer, the means for moving the analytical unit with respect tothe support and movement structure permitting the rotation of theequatorial plane around the equatorial axis, without the support andmovement structure changing its position; and positioning the centre ofthe diffractometer on a point of the surface of an element to beanalyzed.
 13. The method according to claim 12, wherein the analyticalunit has a symmetry plane and the plane is placed perpendicularly to thesurface of the element to be analyzed at the point coincident with thecentre of the diffractometer.
 14. The method according to claim 12,wherein the radiation beam is an x-ray beam.
 15. The method according toclaim 12, wherein the element to be analyzed is not mechanically linkedto the diffractometer.